Downhole well pumps of various types have been developed for both hydrocarbon producing wells and waterwell applications. A typical submersible waterwell pump, for example, may be a single cylinder reciprocating piston type actuated from the surface by an elongated rod or a centrifugal type directly connected to a submersible electric motor supplied with power by way of conductors extending to a power source on the earth's surface. Waterwells of moderate to extreme depths and in low volume producing formations, in particular, are not suitable for centrifugal pumps due to the inefficiency of these pumps at the high working pressures required of moderate to deep wells and rod driven pumps are not suitable because of the weight of the rod and undesirable dynamics of reciprocating very long rods. Moreover, the development of self contained electric power sources, such as photovoltaic power producing units, for remotely located waterwells requires minimizing pump power requirements, particularly when the well pump is required to produce from rechargeable storage batteries or the like, or when required to produce directly from the photovoltaic source.
Accordingly, there has been a strongly increasing need for the development of high efficiency downhole pumps, particularly adapted for waterwell applications, which are reliable, efficient at high working discharge pressures and low pumped volumes, in particular. Although certain other reciprocating piston pumps have been developed as well as power fluid type pumps, these pumps do not have the efficiency or the mechanical reliability for submersed waterwell applications. The present invention has been developed with a view to avoiding the shortcomings of prior art pumps and to solving the needs for high efficiency, high pressure/low volume pumping applications, particularly in low volume waterwells.